Primakov's announcement comes as NATO airstrikes continued for a fifth night, with reports that the police headquarters in Pristina, Kosovo had been hit by bombs.

More than 40 military aircraft took off from the Aviano Air Base in Italy, including at least three U.S. F-117A stealth fighters -- the same type of aircraft as the one that crashed in Yugoslavia during Saturday's fourth day of strikes.

Air raid sirens sounded in Belgrade, but there have been no reports of explosions in the capital so far during this latest wave of NATO firepower. Lights remained on in the city.

After meeting with Yugoslav government and army leaders Sunday, President Slobodan Milosevic said the country would continue its resistance.

In a show of Serb unity, thousands of people attended an anti-NATO rock concert in the center of Belgrade, carrying bulls-eye targets and signs saying "Sorry, we're singing" and referring to NATO as a "New American Terrorist Organization."

Tanjug news agency said the people and armed forces were linked by "strong unity, a high patriotic conscience and determination to endure in the just struggle against the criminal aggressors."

On Sunday, three prominent liberal Russian politicians traveled to Belgrade for a meeting with top Yugoslav leaders, in an attempt to stop the NATO attacks and halt alleged "cleansing" of ethinic Albanians. On Monday morning, they met with Yugoslav Deputy Minister Vuk Draskovic but were notplanning to meet with Yugoslav President Slobodan Milosevic.

At NATO headquarters in Brussels, spokesman Jamie Shea said the bombing campaign is now aimed at heading off what he termed "a major humanitarian disaster" in Kosovo. He said more than 500,000 people -- about a quarter of the province's population -- have been displaced.

Tens of thousands of refugees have headed into the Yugoslav republic of Montenegro and the neighboring nations of Albania and Macedonia, where officials appealed for international help in dealing with the exodus.

Many refugees gave eyewitness accounts of forced expulsions of ethnic Albanians from their homes, summary executions and men being detained and carted away in trucks.

In a telephone interview with CNN from his hiding place near Pristina, Hashim Thaqi, a senior representative of the separatist Kosovo Liberation Army, said Serbian police and paramilitary forces are herding people into concentration camps, conducting mass executions and generally "terrorizing" ethnic Albanians in the province.

He issued a plea for NATO to send in ground troops to stop the killing.

"Only NATO troops can save the people of Kosovo from further catastrophe," Thaqi said. "This is the hour of need for Kosovo."

But leaders of NATO countries have made it clear that they have no plans to introduce troops into the province in a combat role.

Yugoslav officials have denied claims by ethnic Albanians that atrocities are being carried out against civilians in Kosovo. Independent verification of the claims is difficult because most international observers, journalists and humanitarian workers have either evacuated or been expelled from the province.

But senior U.S. and NATO officials, as well as representatives from humanitarian groups, say that a calculated campaign of ethnic cleansing in Kosovo has intensified since the beginning of NATO's military campaign against Yugoslavia.

"Whether we like it or not, we have to recognize we are on the brink of a major humanitarian disaster in Kosovo, the likes of which have not been seen in Europe since the closing days of World War II," Shea said. "We are acting in a just cause. We are convinced of that."

Shea bristled at suggestions that NATO military action may have made the situation worse, noting that Serb actions against ethnic Albanians predated the beginning of the air campaign.

On Sunday, three leading liberal Russian politicians arrived in Belgrade on a peace mission. On their way to the Yugoslav capital, they met with U.S. special envoy Richard Holbrooke in Budapest, Hungary.

The delegation included former Prime Minister Yegor Gaidar, former Vice Premier Boris Nemtsov and former Finance Minister Boris Fyodorov.

In an interview on Russian television Sunday night, one of the trio's liberal colleagues, former Finance Minister Anatoly Chubais, said the peace delegation hopes to serve as a connecting link between Milosevic and Western leaders.

Chubais said they hope to avert a situation where the Kosovo crisis isolates Russia from the West, and he said communists in Russia are trying to play on Russian feelings against the airstrikes.

Chubais said that with the NATO strikes, Western countries are making a "colossal mistake, not only in relationship to us but to itself and the world at large."

Reuters quoted Holbrooke as telling reporters after the meeting that "there is no change in (the American) position in the sense there is a clear disagreement between the Russian government and NATO. But that does not mean we cannot still continue close contacts."

NATO officials announced Saturday that the air campaign would move into a new phase in which the emphasis will be tanks, troop columns and military hardware on the ground in Kosovo.

"Now what we want to do is be able to attack, from the airplanes, their headquarters, their commanders which are underground so that we can stop the tremendous ethnic cleansing which is now taking place on the ground," said NATO Secretary-General Javier Solana on ABC's "This Week" program.

Shea said the attacks will be carried out primarily in Kosovo and areas just to the north of the province, though attacks on air defenses and other military facilities will continue in other parts of Yugoslavia.

Key NATO members Britain and the United States are making more aircraft available for the Yugoslav operation.

The Royal Air Force will commit another 12 combat planes and a tanker to the allied action in the Balkans, and the U.S. Air Force has been given permission to fly more B-52 heavy bombers out of British air bases, British Defense Secretary George Robertson said.

Those planes will be part of NATO's attempt to stop attacks on ethnic Albanians in Kosovo, he said.

The British commitment includes eight Tornado fighter- bombers, four additional Harrier ground attack planes and a tanker, Robertson said. The combat planes will be ready to participate in NATO attacks by Monday.

In Washington, senior U.S. administration officials told CNN that attacks on ethnic Albanians have intensified since the NATO airstrikes began.

"This is not just one unit out of control," said one official. "This is an calculated campaign by the (Yugoslav) government to reduce or eliminate the Albanian population of Kosovo.

"Clearly, a catastrophe is unfolding," he said.

U.S. officials said they believe much of the Kosovar Albanian political leadership, including Ibrahim Rugova, have gone into hiding.

But in an interview with CNN's "Late Edition," Vuk Draskovic, Yugoslavia's deputy prime minister, denied that there was any orchestrated campaign under way to kill ethnic Albanians or force them out of the country.

"We need Albanians in our state. No one has that genocide strategy. Albanian (terrorists) are doing that crime," he said.

In a press briefing on Saturday's NATO attacks, Air Commodore David Wilby, a British member of NATO's staff, said the strikes were concentrated near Belgrade, with other strikes running south in a line through Pristina to the Macedonian border.

The attacks were carried out "without significant collateral damage to civilian life or infrastructure," Wilby said. Sixty-six NATO aircraft attacked in two waves, striking 17 major targets.

Allied forces flew a total of 253 sorties, hitting 11 targets in the region of Belgrade and six others scattered across the country, he said.

For the most part, those targets were parts of Yugoslavia's integrated air defense system and command-and-control headquarters, and headquarters of Serbia special police units, who are believed responsible for much of the violence reportedly taking place in Kosovo.

During Saturday's operations, one U.S. F-117A stealth fighter crashed about 40 kilometers (25 miles) west of Belgrade. An American search-and-rescue team found the pilot, who was reported in good condition Sunday at a NATO base. Pentagon officials say they have not determined why the plane crashed.

Meanwhile, Reuters quoted a senior government officials in Macedonia as saying that country was expected to ask NATO to admit it urgently as a member because of security concerns over the crisis in Kosovo on its northern border.

NATO began the airstrikes Wednesday after the Milosevic government refused to sign a pact ending a year of ethnic strife in Kosovo. Representatives of the province's ethnic Albanian population already have signed the agreement.